Dealing now on a new 5th wheel, and planning for power setup.
Will be on a dry permanent site. Unit has a residential fridge with factory 1000 watt dedicated inverter. Wanting to also power other outlets. Can I add another 1000 watt inverter for that, or get a bigger one to cover all? Any new inverter will be inverter/charger.
Looking at 4x6 volt batteries, and 530 watts solar, MPPT controller.

Off the cuff I'd go with more batteries and a backup charging method. However I'm from gloomy Michigan where weeks can go by without sunlight. 4x 6v batteries are going to get wiped out in days powering a residential fridge.

Since this is a permanent site, can you build an external battery box? 12 to 16x GC2 would be a start. Consider 48v or higher for your system voltage. It makes the wiring much easier for the inverter and solar.

For small stuff the existing 1000 will do fine. Coffee, microwave, hairdryer you need another 2000 watts sine wave. If going over 2000 watts I recommend stepping up to 24 or 48 volts to drive it. 4x GC2 will be small. If you are full time I would be looking at lithium and more solar.

You should not get that res fridge! Your life will be so much more enjoyable with a propane fridge so you can relax. Very serious about that. Res fridge is only for when on shore power or a couple days off grid. Not for several days and longer off grid.

Just get one of those giant propane bottles delivered and the propane truck comes by once in a long while as needed.

Even so, as said above you want a 2000w or more inverter to run the MW (pulls 130 or more DC amps) A 1000 will just barely run a toaster (pulls 90 DC amps.)

Totally agree with BFL. Resi fridges are fine for their intended use but boon docking under those conditions will be a lot more bother with one. I would definitely go with the PP fridge.
If you do keep the resi fridge, don't count on pulling a lot of power from its inverter. It will be busy starting that big fridge.